With the popularity of the Internet and development of mobile communications, users increasingly need to be able to access the Internet at anytime and anywhere, which causes provision of mobile Internet access to become one of hotspots of Internet technology research. Mobile IP is a solution supporting movement of a node provided on the basis of original IP protocol, which enables people to be able to connect to the Internet at anytime via terminals like notebook computer, PDA (personal digital assistant) or the like, no matter where he/she is, for example at home, on a train or airplane. It is important that as the movement of the location of a user terminal, the user terminal's IP address remains unchanged, regardless of where the mobile device is actually located. Thus enable other devices to be able to access the user terminal with this IP address, consequently maintaining the continuity of communication during the movement. Therefore, the Mobile IP achieves free access to the Internet by users.
As shown in FIG. 1, the IPv4-based Mobile IP defines three functional entities: Mobile Node MN, Home Agent HA and Foreign Agent FA. The Mobile Node MN is a mobile terminal which may change its network attachment point by moving, such as notebook computer. PDA, cell phone, etc. The MN has a Home Address HoA in its home network, and the Home Address HoA which is fixed as other addresses of fixed hosts is provided by the Home Network HN. For a Mobile Node which has moved, regardless of where its current attachment point is, the Mobile Node still seems to be connected to the Home Network from the perspective of other devices in the network. The Home Agent is a node located within the Home Network of the Mobile Node, typically, it is a router. When the Mobile Node leaves the Home Network and enters into a Foreign Network, it registers its obtained care-of address with the Home Agent. The Home Agent keeps the current location information of the Mobile Node, and when intercepting data packets destined to the home address of the Mobile Node, tunnels the data packets to the Mobile Node. The Foreign Agent FA is a host in a Foreign Network when the Mobile Node moves to the Foreign Network FN, usually, it is a router which may provide routing services for Mobile Nodes and may also release the tunnel encapsulation for the tunneled packets from the HA of the MN and send the de-encapsulated data packets to MN. Both the HA and FA may periodically send an agent advertise message from which MNs can determine whether they are located in the Home Network HN or the Foreign Network FN. When a Mobile Node is in FN, a care-of address CoA can be obtained from the received foreign agent advertise message, such as Foreign Agent care-of address. Also, a care-of address can also be allocated by a Foreign Network, such as Co-located care-of address CoCoA. Wherein, the CoCoA is a separate IP address allocated by the FN to the MN, and the Mobile Node may receive tunneled packets with encapsulation. The Mobile Node using the FACoA then receives de-encapsulated packets forwarded by the FA.
In the IPv4 environment, each time the MN moves from one of foreign agents to another, it registers the care-of address to its Home Agent. Therefore, in order to keep the continuity of a session, handover delay of the network-layer handover and packet loss need to be reduced to the minimum. The existing technology acquires seamless network-layer handover mainly by two manners. The first one is to directly reduce the possible delay of the procedures needed in handover, e.g. for reducing the delay of some procedures in handover, overlapping several procedures in the handover to reduce the overall handover delays (i.e., Registration in advance). However, it is difficult to get a seamless network-layer handover merely by the first manner. For example, if the distance between the Foreign Network and the Home Network of the Mobile Node is too large, the signaling delay for a registration may be very long.
As shown in FIG. 2, the second manner is Regional Registration Solution. In this solution, in order to reduce registration, a new network element named Gateway Foreign Agent GFA is added in the FN. The Gateway Foreign Agent as the central node is responsible for the maintaining and distributing a list of visitors, and forwarding data. In control plane, all the registration requests transmitted from MN to Home Agent HA are forwarded by the current FA to the GFA, and the GFA further determines whether it is necessary to forward the registration requests to HA. Moreover, the Gateway Foreign Agent collects and maintains all the visitor information and distributes it to other foreign agents in the visited domain. U.S. Patent US7069338B2 details the Regional Registration Solution, and details for the solution are not described here any more. Thus, the topology between the Gateway Foreign Agent and associated all foreign agents of regional registration located within the same visited domain is fixed, which lacks flexibility in deployment. Moreover, the solution requires not only setting an additional Gateway Foreign Agent in the network, but also the regional-registration-related function being supported in the Home Agent HA, Foreign Agent FA as well as Mobile Node MN, which will greatly increase implementation cost, prone to be rejected by most vendors and operators. Also, the drawbacks difficult to overcome by the solution are: for existing MNs, they can not benefit from the solution because they can not support the corresponding regional registration function; for existent HAS and FAs, they can not be integrated into this solution, because they can not support the corresponding function, too.
As it can be seen, an improved solution is still needed in order to achieve the minimization of the number of signaling messages arriving at the Home Network, thus reducing the signaling delay produced when the MN is moving in the FN.